Field of the Invention
The present disclosure relates to image forming apparatuses such as copying machines, printers, and facsimile machines using an electrophotographic system or an electrostatic recording system.
Description of the Related Art
Image forming apparatuses using an electrophotographic method or the like in the related art perform an operation of charging a photosensitive member and an image bearing member serving as an electrostatic recording dielectric by discharge. Known examples of the method for charging an image bearing member by discharge include a corona charging method and a contact charging method. In particular, the contact charging method is often employed in recent years because of the advantages of low level ozone emission and low power consumption. The contact charging method charges the surface of an image bearing member by a discharge that occurs in a minute gap between the image bearing member and a charging member in contact with the image bearing member by applying a voltage higher than a charging start voltage to the charging member. As an example of the charging member, a charging roller is widely used in the viewpoint of its excellent charging stability.
In the method of charging the image bearing member by discharging, discharge products such as ozone and nitrogen oxides (NOx) are generated, and the discharge products adhere to the surface of the image bearing member. In the contact charging method, the amount of discharge is smaller than that of the corona charging method using a corona charger, so that the amount of discharge products is small. However, in the contact charging method, discharge products are generated in a minute gap between the image bearing member and the charging member. Therefore, even if the discharge products generated is a little, the discharge products adhere to the surface of the image bearing member. When the discharge products adhere to the surface of the image bearing member, the discharge products absorb moisture to decrease the electrical resistance of the surface of the image bearing member, decreasing the charge holding capability of the image bearing member. This can cause a phenomenon called “image deletion” in which electrostatic latent images are chipped, blurred, or smeared.
Known examples of a method for reducing those influences of the discharge products include: a method of drying the surface of the image bearing member by increasing the temperature of the surface of the image bearing member with a heater disposed inside or in the vicinity of the image bearing member, a method of removing the discharge products by rotating the image bearing member while no image is being formed to increase the number of times of friction between the image bearing member and a cleaning member per unit time; a method of providing an abrasive material to the surface of the image bearing member to increase the image-bearing-member abrasive ability of the cleaning member; and a method of providing a releasing agent for enhancing the releasability to the surface of the image bearing member to make it difficult for the discharge products to adhere to the surface of the image bearing member.
The operations for reducing the influence of the discharge products described above are preferably executed when image deletion is likely to occur in order to reduce or eliminate wasteful consumption of energy and materials, wearing of the components, and a decrease in image productivity. The image deletion tends to occur in a severe use environment, for example, when the image forming apparatus is under high temperature and high humidity conditions, or when the image forming apparatus performs a printing operation for a long time. For that reason, a method of detecting a state in which image deletion is likely to occur and executing the above operations for reducing the influence of the discharge products only when needed has been proposed.
Japanese Patent Laid-Open No. 2010-113103 discloses a method of executing an image-deletion suppressing mode only when a state in which image deletion is likely to occur is detected. The method disclosed in Japanese Patent Laid-Open No. 2010-113103 detects the state in which image deletion is likely to occur using the fact that, when discharge products adhere to the surface of the image bearing member, the image bearing member is slightly charged even when a direct-current (DC) voltage less than the charge staring voltage is applied to the charging member. This method can be implemented by providing a detection circuit for detecting a current value or a voltage value when a DC voltage less than the discharge starting voltage is applied to the charging member. This eliminates the need for disposing a potential sensor for detecting the surface potential of the image bearing member around the image bearing member, which is advantageous for reducing the size and cost of the apparatus.
The above methods for reducing the influence of the discharge products, such as heating with a heater, abrasion using a cleaning member, and supplying a releasing agent, individually have a certain effect. However, according to the study of the inventors, the methods still need improvements in the viewpoint of simplification of the apparatus configuration and reduction in necessary materials. In particular, there is a cleanerless image forming apparatus that does not include a dedicated cleaning unit for removing a developer remaining on the surface of the image bearing member after a transfer process. In the cleanerless image forming apparatus, since no friction occurs between the cleaning member and the image bearing member, discharge products are likely to adhere to the surface of the image bearing member and to accumulate thereon, and the method for removing the discharge products using the friction between the cleaning member and the image bearing member cannot be used. For those reasons, a method that is advantageous for simplifying the apparatus configuration and reducing the number of necessary components and can be used in a cleanerless image forming apparatus is required.
In order to reduce or eliminate wasteful consumption of energy and materials, wearing of the components, and a decrease in image productivity, it is desirable to execute the operation for reducing the influence of discharge products when the image bearing member enters a state in which image deletion is likely to occur and to promptly complete the operation after the state is remedied. However, the method disclosed in Japanese Patent Laid-Open No. 2010-113103 executes a certain image-deletion suppressing mode when detecting the state in which image deletion is likely to occur. For that reason, the control may take more time than necessary to decrease the image productivity.